title: A case of rectal tumor in which the shape altered with regression in short period.
abstract: BACKGROUND
  Histological regression of solid tumors in adults receiving no treatment is rare. Specifically, spontaneous partial and complete regression of colorectal cancers account for less than 2% of such cases and those without metastasis are exceedingly rare.
  
  
  METHODS
  A 60-year-old male underwent total colonoscopy following a positive fecal occult blood test at the referring hospital. A flat elevated lesion with central reddish depression, 10 mm in diameter, was detected in the lower rectum. Biopsy results from the referring hospital showed a well-differentiated adenocarcinoma and the patient was referred to our hospital for diagnosis and treatment. Preoperative colonoscopy was performed to determine the therapeutic strategy; however, we found only scar tissue and there were no endoscopic features to suggest malignancy. Biopsy from the scar revealed normal rectal mucosa and we performed diagnostic endoscopic submucosal resection with a ligation device (ESMR-L) one week later. The resected specimen showed a 1 mm well-differentiated adenocarcinoma with low-grade atypia and no lymphovascular invasion. The macroscopic type was 0-IIb, the depth of invasion was intramucosal, and the vertical and lateral margins were negative. There has been no evidence of recurrence for 18 months following treatment.
  
  
  CONCLUSIONS
  We report a case of a rectal tumor showing regression over a short period without treatment. Spontaneous regression of malignant tumors is a rare and unexplained phenomenon. Further research and understanding of the mechanism holds the key for treatment and prevention of cancer in the future.
authors.affiliation: Endoscopy Division, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan. tamatsud@ncc.go.jp.
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Nakamura
authors.forename: Taku
authors.initials: T
authors.lastname: Sakamoto
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nakajima
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Saito
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Taniguchi
authors.forename: Takahisa
authors.initials: T
authors.lastname: Matsuda
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology*; D003113:Colonoscopy; D006801:Humans; D007413:Intestinal Mucosa / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D009365:Neoplasm Regression, Spontaneous / Q000473:pathology*; D012004:Rectal Neoplasms / Q000473:pathology*